This invention relates to a tool for use in servicing a component in, or a section of, a pipeline such as a wellhead spool outlet. The invention is particularly, although not exclusively applicable to a tool the use of which enables the installation and removal of a plug in a wellhead spool outlet under pressure control, though it could be useful for other servicing operations in such a location. The tool is moreover particularly intended for enabling such servicing to be carried out in restricted access space situations.
In a wellhead spool outlet or other casing head, tubing head or christmas tree outlet on a wellhead, it is often necessary to replace or service a valve, e.g. a gate valve installed in-line. There may be two or three such valves (or other equipment) installed in series. In order to isolate that valve or that section of pipeline incorporating it, a screw-threaded bore will have been provided at the time of installation, located in a flange situated immediately upstream of the valve or pipe section; this bore is intended to receive a screw-threaded control plug which when screwed into place completely closes off the wellhead pressure from that section. This then enables the valve or other equipment to be serviced or replaced as required, quite safely because it is isolated from the wellhead pressure. The fitting of the screw-threaded plug into the tapped isolating flange bore and the removal of the plug afterwards is carried out by means of a special tool and it is such a tool with which the present invention is primarily concerned.
A known tool of this type comprises a yoke shaped body in which is slidably and rotatably mounted a polished rod, the forward end of which projects beyond a mounting flange of the body and has a socket head into which a corresponding square or hexagonal spigot of a control plug, which is to be fitted, can be inserted. The rod is surrounded by pressure-tight glands within the body and its other end extends into an elongate tubular casing fastened to the body, which casing can, in use, be pressurized by hydraulic or pneumatic pressure so as to apply an axial force on the rod to balance the operating pressure of the spool outlet. Indeed, in some cases the same pressure fluid is used, fed by a tapping from the wellhead spool outlet to the rod casing.
To use the tool, a valve in the spool outlet is closed, a blanking service flange is removed and the service tool (with a control plug securely held on the rod socket end) is bolted on by means of its end flange. The rod casing then has pressure fluid admitted to it to balance the wellhead spool pressure and when this balance is reached (as indicated by suitable gauges), the valve and any other valves in line are opened. Owing to the fact that the pressures on the rod are balanced, the rod may now be advanced by applying a suitable wrench against an exposed portion of the rod in the yoke-shaped part of the tool body, the rod being pushed forward so that the control plug carried at its front end is advanced through the open valve or valves until it reaches the tapped bore in the isolating flange whereupon the rod is rotated to screw the plug into place. After checking that the wellhead pressure is safely isolated from the spool outlet, the valve which requires servicing may safely be dismantled or repaired.
After completing the valve servicing, the plug installation procedure is reversed, inserting the rod until its socket end engages the plug, unscrewing the plug and withdrawing it through the open valves, the plug being carried on the end of the polished rod which is readily slidable in the tool body and casing under the balanced fluid pressure as explained above.
Wellhead spool outlet sections may be of considerable size, with several valves of 2 inch (51 mm) or more, in line, and in order to reach right along inside the spool section to insert a control plug it is obviously necessary to use a sufficiently long rod. In some cases, the rod itself may need to be over 3 feet (912 mm) long, and of course in its retracted position this means that the combined length of the tool body and its casing must also be about the same dimension in order to accommodate that rod length before the rod is inserted.
Where the wellhead surroundings are clear and access is unrestricted, this is no problem, and a suitably sized tool with a solid rod of the appropriate length can be used. However, there are situations where access space is restricted. These situations are likely to be found on production platforms with minimum well slot centers, or annulus valves on land installations within deep cellars. In such situation a different type of servicing tool is required which is compact, in which there is a relatively short rod which can be advanced by suitable drive means and to which may be added a number of similar relatively short rod extensions, the rod being advanced and held, in stages, whilst successive extensions are added.
A tool of the prior art included moving and fixed crossheads enabling rod extension pieces to be fitted for extending the rod in stages, to thereby avoid the need for a solid rod of sufficient length to reach right along the pipeline to the plug insertion bore. A valve removal tool with such a long solid rod could not be fitted in circumstances where space around the wellhead is restricted. Such earlier tool did not include any safety stop means or collet lock means.